Success ! a minimalist, single-MOSFET quartz oscillator !

A project log for Yet Another (Discrete) Clock

I HAD to finally do this basic "exercice de style" in digital electronics, using some hundreds of transistors and diodes...

Yann Guidon / YGDESYann Guidon / YGDES 05/26/2016 at 21:104 Comments

My quest is finally over !

I didn't believe it when I wrote Impendance matching for crystal oscillators but I had to try it and it worked !

This circuit fits all my requirements:

Yes, only 3 additional parts (not counting the decoupling capacitor), my precedent theory seems to work !

The downsides are a) slow/lazy startup and b) 3rd harmonics but they are not critical flaws.

(trace: 1V/div)

The resistors need some tuning to adjust the waveform amplitude and offset but nothing too hard thanks to a simple 'scope. I don't see how to reduce the 3rd harmonics but I don't care much now.

I wish I knew a better way to start the oscillation than tapping it.



SHAOS wrote 05/27/2016 at 00:29 point

Wow - so simple! :)

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Yann Guidon / YGDES wrote 05/27/2016 at 00:45 point

Even I have a hard time to believe it but the 'scope doesn't lie :-)

However for the Germanium case, the dual-stage amplifier is ok for low-gain, slow transistors and i'll stick to it. This is the circuit that made me realise that an oscillator doesn't have to use an inverter, and a non-inverting amplifier also works. So if a non-inverter works, why not loop the common-gate amplifier on itself ?

I'm still trying to get my head around it :-D

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K.C. Lee wrote 05/26/2016 at 23:05 point


>I wish I knew a better way to start the oscillation than tapping it.
All you need is an initial pulse of some kind. Some kind of power on R-C circuit on the gate of the MOSFET?  

All else failed, use the vibration of a relay or a pager motor on power up. :)

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Yann Guidon / YGDES wrote 05/26/2016 at 23:18 point

Hopefully, nothing mechanical ;-)

The "pulse" could be another MOSFET short-circuiting the Z resistor.

It could be triggered by a astable oscillator that sends short pulses (20µs ?) every hundreds of millisecond, but could be reset when oscillations are detected, further down in the divider circuits.

I have to find 2.5V voltage references as well...

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